Vertical structure nonvolatile memory devices

ABSTRACT

A vertical structure nonvolatile memory device can include a channel layer that extends in a vertical direction on a substrate. A memory cell string includes a plurality of transistors that are disposed on the substrate in the vertical direction along a vertical sidewall of the channel layer. At least one of the plurality of transistors includes at least one recess in a gate of the transistor into which at least one protrusion, which includes the channel layer, extends.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2010-0052366, filed on Jun. 3, 2010, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

The inventive concept relates to nonvolatile memory devices, and moreparticularly, to nonvolatile memory devices having a vertical channelstructure.

Electronic appliances are becoming smaller in size, while maintaininghigh data throughput. Non-volatile memory devices may use a verticaltransistor structure to increase integration levels.

SUMMARY

Embodiments according to the inventive concept can provide verticalstructure nonvolatile memory devices. Pursuant to these embodiments, avertical structure nonvolatile memory device can include a channel layerthat extends in a vertical direction on a substrate. A memory cellstring includes a plurality of transistors that are disposed on thesubstrate in the vertical direction along a vertical sidewall of thechannel layer. At least one of the plurality of transistors includes atleast one recess in a gate of the transistor into which at least oneprotrusion, which includes the channel layer, extends.

In some embodiments according to the inventive concept, the plurality oftransistors of the memory cell string can include a plurality of memorycell transistors, and at least one selection transistor that is disposedat one end, or at both ends, of the memory cell string. In someembodiments according to the inventive concept, the at least one recessand at least one protrusion are included in the at least one selectiontransistor. In some embodiments according to the inventive concept, anentire width of the channel layer protrudes into the recess and isconformally on a surface of the recess. In some embodiments according tothe inventive concept, the at least one protrusion only protrudes into amiddle region of the gate between uppermost and lowermost surfaces ofthe gate adjacent to respective interlayer insulating layers.

In some embodiments according to the inventive concept, the recess has avertical dimension that is greater than all of a remaining verticaldimension of the gate outside the recess. In some embodiments accordingto the inventive concept, the at least one recess and the at least oneprotrusion includes first and second recesses and first and secondprotrusions that are disposed in first and second regions of the gate.

In some embodiments according to the inventive concept, the structurecan also include a first interlayer insulating layers located betweenimmediately adjacent gates. A second interlayer insulating layer can bein the recess between a gate electrode of the gate and the channel thechannel layer. In some embodiments according to the inventive concept,the second interlayer insulating layer is between the channel layer andthe gate electrode and has an etch selectivity that is different fromthat of the first interlayer insulating layers.

In some embodiments according to the inventive concept, the firstinterlayer insulating layers are recessed from sides of the gatesadjacent to the channel layer, in the same direction as the direction inwhich the at least one protrusion extends into the recess. In someembodiments according to the inventive concept, the gate can include atunneling insulating layer, a charge storage layer and a blockinginsulating layer that are sequentially stacked on the channel layer anda gate electrode

In some embodiments according to the inventive concept, a verticalstructure nonvolatile memory device can include a plurality oftransistors in a memory cell string, where each includes a respectivegate electrode. A recess can be included in at least one of the gateelectrodes to define a portion of a non-planar surface of the at leastone gate electrode. A channel layer can protrude into the recess and isconformally on the portion of the non-planar surface. In someembodiments according to the inventive concept, the at least one of thegate electrodes is only first and second selection transistors at bothends of the memory cell string.

In some embodiments according to the inventive concept, the recess is afirst recess and the portion is a first portion where the device furtherincludes a second recess in the least one of the gate electrodesincluding the at least one recess that defines a second portion of thenon-planar surface therein. The channel layer protrudes into the secondrecess and is conformally on the second portion of the non-planarsurface.

In some embodiments according to the inventive concept, a system caninclude a memory that includes a vertical structure nonvolatile memorydevice which can include a plurality of transistors in a memory cellstring, where each includes a respective gate electrode. A recess can beincluded in at least one of the gate electrodes to define a portion of anon-planar surface of the at least one gate electrode. A channel layercan protrude into the recess and can be conformally on the portion ofthe non-planar surface. The system can further include a processorconfigured to communicate with the memory via a bus and an input/outputunit that can be configured to communicate with the bus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an equivalent circuit diagram of a memory cell array of anonvolatile memory device in some embodiments according to the inventiveconcept.

FIG. 2 is a cross-sectional view of a vertical structure nonvolatilememory device in some embodiments according to the inventive concept.

FIGS. 3 through 10 are cross-sectional views describing methods offabricating the nonvolatile memory device in some embodiments accordingto the inventive concept.

FIGS. 11 and 12 are plan views illustrating the relative positions ofchannel layers with respect to bit lines in the vertical structurenonvolatile memory device in some embodiments according to the inventiveconcept.

FIG. 13 is a cross-sectional view of a vertical structure nonvolatilememory device in some embodiments according to the inventive concept.

FIGS. 14 through 16 are graphs illustrating the results of simulation ofpotential distribution in the vertical structure nonvolatile memorydevice of FIG. 13.

FIG. 17 is a cross-sectional view of a vertical structure nonvolatilememory device in some embodiments according to the inventive concept.

FIG. 18 is a cross-sectional view of a vertical structure nonvolatilememory device in some embodiments according to the inventive concept.

FIG. 19 is a cross-sectional view of a vertical structure nonvolatilememory device in some embodiments according to the inventive concept.

FIGS. 20 through 23 are cross-sectional views for describing a method offabricating the vertical structure nonvolatile memory device of FIG. 19.

FIG. 24 is a block diagram of a nonvolatile memory device in someembodiments according to the inventive concept.

FIG. 25 is a schematic view illustrating a memory card according in someembodiments according to the inventive concept.

FIG. 26 is a block diagram of an electronic system in some embodimentsaccording to the inventive concept.

DESCRIPTION OF EMBODIMENTS ACCORDING TO THE INVENTIVE CONCEPT

The inventive concept will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown.

This invention may, however, be embodied in many different forms andshould not be construed as limited to the exemplary embodiments setforth herein. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the invention to those of ordinary skill in the art.

It will be understood that when an element or layer is referred to asbeing “on” another element or layer, the element or layer can bedirectly on another element or layer or intervening elements or layers.In contrast, when an element is referred to as being “directly on”another element or layer, there are no intervening elements or layerspresent. In the drawings, lengths and sizes of layers and regions may beexaggerated for clarity. Like reference numerals refer to like elementsthroughout. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items.

The terms used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,components, and/or groups thereof, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

It will be understood that, although the terms first, second, third,etc., may be used herein to describe various elements, components,regions, layers and/or sections, these elements, components, regions,layers and/or sections should not be limited by these terms. These termsare only used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the inventive concept.

Embodiments of the invention are described herein with reference toillustrations that are schematic illustrations of idealized embodiments(and intermediate structures) of the invention. As such, variations fromthe shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, are to be expected. Thus,embodiments of the invention should not be construed as limited to theparticular shapes of regions illustrated herein but are to includedeviations in shapes that result, for example, from manufacturing.

Hereinafter, embodiments of vertical structure nonvolatile semiconductormemory devices according to the inventive concept will be described withreference to nonvolatile NAND flash memory devices. Vertical structurenonvolatile memory devices can retain stored data even when power is notsupplied.

FIG. 1 is an equivalent circuit diagram of a memory cell array of anonvolatile memory device in some embodiments according to the inventiveconcept.

Referring to FIG. 1, the memory cell array 10 includes a plurality ofmemory cell strings 11. Each memory cell string 11 may have a verticalstructure extending substantially perpendicular to a main surface of asubstrate. The plurality of memory cell strings 11 may constitute amemory cell block 13.

Each of the plurality of memory cell strings 11 includes a plurality ofmemory cells MC1-MCn, a string selection transistor SST, and a groundselection transistor GST. The ground selection transistor GST, thememory cells MC1-MCn, and the string selection transistor SST of each ofthe memory cell strings 11 may be serially arranged in a verticaldirection. The plurality of memory cells MC1-MCn may store data. Aplurality of word lines WL1-WLn are connected to the memory cellsMC1-MCn, respectively, to control the memory cells MC1-MCn. The numberof memory cells MC1-MCn may vary according to the capacity of thenonvolatile memory device.

The memory cell strings 11 are respectively arranged in 1^(st)-m^(th)columns of the memory cell block 13. One end of each of the memory cellstrings 11, for example drain sides of the respective string selectiontransistors SST, may be respectively coupled to a plurality of bit linesBL1-BLm. The other end of each of the memory cell strings 11, forexample source sides of the ground selection transistors GST, may becoupled to a common source line CSL.

A plurality of word lines WL1-WLn may be respectively coupled to rows ofthe memory cells MC1-MCn of the plurality of memory cell strings 11.Data may be written to or may be read (or erased) from the plurality ofmemory cells MC1-MCn upon activation of the word lines WL1-WLn.

The string selection transistors SST of the memory cell strings 11 maybe arranged between the corresponding bit lines BL1-BLm and the memorycells MC1-MCn. String selection lines SSLs are respectively coupled tothe gates of the string selection transistors SST, and thus may controldata transfer between the bit lines BL1-BLm and the memory cells MC1-MCnin the memory cell block 13.

The ground selection transistors GST may be arranged between the commonsource line CSL and the plurality of memory cells MC1-MCn. Groundselection lines GSL are respectively coupled to the gates of the groundselection transistors GST, and thus may control data transfer betweenthe common source line CSL and the memory cells MC1-MCn in the memorycell block 13.

FIG. 2 is a cross-sectional view of a vertical structure nonvolatilememory device in some embodiments according to the inventive concept.

Referring to FIG. 2, the nonvolatile memory device 1 includes asubstrate 100 whose main surface extends in a first direction (i.e., anx-axis direction in FIG. 2). The substrate 100 may contain asemiconductor material, for example, a Group IV semiconductor, a GroupIII-V compound semiconductor, or a Group II-VI oxide semiconductor.Examples of the Group IV semiconductor include silicon, germanium, andsilicon-germanium. The substrate 100 may be a bulk wafer or an epitaxiallayer.

A channel layer 140, including a protrusion, extends on the substrate100 in a second direction (i.e., a y-axis direction of FIG. 2)substantially perpendicular to the first direction in which the mainsurface of the substrate 100 extends. A gate insulating layer 157 isdisposed on a portion of the channel layer 140. The channel layer 140may be in the form of an annular pillar filled with a channel holeinsulating layer 115.

A plurality of transistors 170 are vertically disposed on an uppersurface of the substrate 100 in the second direction (i.e., the y-axisdirection of FIG. 2) along the channel layer 140. One channel layer 140and the plurality of transistors 170, which are disposed in the seconddirection along the channel layer 140 constitute one of the memory cellstrings 11 (see FIG. 1).

Each of the memory cell strings 11 (see FIG. 1) includes a plurality offirst transistors 172, which constitute a plurality of memory cells, andsecond transistors 176 and 178, which constitute selection transistors.In the nonvolatile memory device 10 having the configuration of FIG. 1,the second transistors 176 and 178 of each of the memory cell strings 11may include one ground selection transistor 176 and one string selectiontransistor 178.

A bit line may be coupled to the string selection transistor 178, whichconstitutes the second transistors 176 and 178, as illustrated inFIG. 1. The bit line may extend in a linear pattern in the firstdirection (the x-axis direction of FIG. 2). The bit line may be coupledto one of the selection transistors 176 and 178, for example, the stringselection transistor 178, via a contact.

The channel layers 140 have protrusions extending in the first direction(the x-axis direction in FIG. 2). Gates 150, including the gateinsulating layer 157 and a gate electrode 159, have uneven structuresconforming to the protrusions of the channel layers 140. As used herein,the term “uneven structure” refers to both a protrusion and a recesshaving an opposite pattern to the protrusion. The protrusions of thechannel layers 140 may be located in the middles of the gates 150, i.e.,between upper and lower portions of the gates 150 disposed on thesubstrate 100 in a vertical direction. The protrusions may have avertical dimension that is larger than those of upper and lower portionsof the gates 150 divided by the protrusions. The protrusions of thechannel layers 140 may also extend in a third direction (i.e., a z-axisdirection of FIG. 2). The protrusions of the channel layers 140 may havedimensions in the first direction (the x-axis direction of FIG. 2) thatare smaller than the dimensions of the transistors 170. The unevenstructures of the gates 150 may have any of various lengths and shapes,and are not limited to the exemplary embodiment illustrated in FIG. 2.

It will be understood that the uneven structure can define at least onerecess in the surface of the gate 150 where the channel layer 140conformally protrudes into the recess. The recess, therefore, definesthe profile of the gate surface at the channel layer 140 as beingnon-planar.

The plurality of first transistors 172 among the plurality oftransistors 170, which constitute the plurality of memory cells, mayrespectively include the gates 150, which include the gate insulatinglayer 157 and the gate electrode 159 sequentially disposed on a sidewallof the channel layers 140.

The selection transistors 176 and 178 among the plurality of transistors170 may respectively include the gates 150, which include the gateinsulating layer 157 and the gate electrode 159 sequentially disposed onthe sidewall of the channel layers 140.

The gate insulating layer 157 may have a stack structure in which atunneling insulating layer 152, a charge storage layer 154 and ablocking insulating layer 156 are sequentially stacked on the sidewallof the channel layers 140 in the order stated.

The tunneling insulating layer 152 may be a single layer or amulti-layer including at least one material selected from the groupconsisting of silicon oxide (SiO₂), silicon nitride (Si₃N₄), siliconoxynitride (SiON), hafnium oxide (HfO₂), hafnium silicon oxide(HfSi_(x)O_(y)), aluminum oxide (Al₂O₃), and zirconium oxide (ZrO₂).

The charge storage layer 154 may be a charge trapping layer or afloating gate conductive layer. When the charge storage layer 154 is afloating gate conductive layer, the charge storage layer 154 may beformed using chemical vapor deposition (CVD). For example, the chargestorage layer 154 may be formed by causing a SiH₄ or Si₂H₆ gas and a PH₃gas to flow by using low-pressure chemical vapor deposition (LPCVD) todeposit polysilicon. When the charge storage layer 154 is a chargetrapping layer, the charge storage layer 154 may be formed as a singlelayer or a multi-layer including at least one material selected from thegroup consisting of silicon oxide (SiO₂), silicon nitride (Si₃N₄),silicon oxynitride (SiON), hafnium oxide (HfO₂), zirconium oxide (ZrO₂),tantalum oxide (Ta₂O₃), titanium oxide (TiO₂), hafnium aluminum oxide(HfAl_(x)O_(y)), hafnium tantalum oxide (HfTa_(x)O_(y)), hafnium siliconoxide (HfSi_(x)O_(y)), aluminum nitride (Al_(x)N_(y)), and aluminumgallium nitride (AlGa_(x)N_(y)). The charge storage layer 154 mayinclude quantum dots or nanocrystals. In this regard, the quantum dotsor nanocrystals may include fine particles of a conductor, such as ametal or a semiconductor.

The blocking insulating layer 156 may be formed as a single layer or amulti-layer including at least one material selected from the groupconsisting of silicon oxide (SiO₂), silicon nitride (Si₃N₄), siliconoxynitride (SiON), and a high-k dielectric material. The blockinginsulating layer 156 may be formed of a higher-k dielectric materialthan the tunneling insulating layer 152. The higher-k dielectricmaterial may include at least one material selected from the groupconsisting of aluminum oxide (Al₂O₃), tantalum oxide (Ta₂O₃), titaniumoxide (TiO₂), yttrium oxide (Y₂O₃), zirconium oxide (ZrO₂), zirconiumsilicon oxide (ZrSi_(x)O_(y)), hafnium oxide (HfO₂), hafnium siliconoxide (HfSi_(x)O_(y)), lanthanum oxide (La₂O₃), lanthanum aluminum oxide(LaAl_(x)O_(y)), lanthanum hafnium oxide (LaHf_(x)O_(y)), hafniumaluminum oxide (HfAl_(x)O_(y)), and praseodymium oxide (Pr₂O₃).

The gate electrode 159 may be formed as a single layer or a multi-layerincluding at least one material selected from the group consisting ofpolysilicon, aluminum (Al), gold (Au), beryllium (Be), bismuth (Bi),cobalt (Co), hafnium (Hf), indium (In), manganese (Mn), molybdenum (Mo),nickel (Ni), lead (Pb), palladium (Pd), platinum (Pt), rhodium (Rh),rhenium (Re), ruthenium (Ru), tantalum (Ta), tellurium (Te), titanium(Ti), tungsten (W), zinc (Zn), and zirconium (Zr).

Impurity regions 105 may be defined in the upper surface of thesubstrate 100. The impurity regions 105 may be coupled to the commonsource line (CSL) 180. The impurity regions 105 may also form PNjunctions with other regions of the substrate 100. The length of thecommon source lines (CSL) 180 in the second direction (the y-axisdirection of FIG. 2) are not limited to the exemplary embodimentillustrated in FIG. 2. For example, the common source lines (CSL) 180may be shorter than those illustrated in FIG. 2. Spacers 117 of aninsulating material may be disposed on the sidewalls of the commonsource lines (CSL) 180.

The channel layers 140 may be sequentially doped with impurities havingthe same conductivity type to define a series of wells or channels thatcontribute to the operation of the plurality of memory cells MC1-MCn. Inthis case, during a writing or reading operation, the memory cellsMC1-MCn may be connected via field effect sources/drains. Surfaces ofthe channel layers 140 between the memory cells MC1-MCn may be turned onusing a lateral electric field, i.e., a fringing field, of the gateelectrodes 159. This may also apply to the channel layers 140 betweenthe string selection transistors 178, and to the channel layers 140between the ground selection transistors 176.

Interlayer insulating layers 110 may be disposed on the channel layers140 between the plurality of transistors 170, including the firsttransistors 172 and the second transistors 176 and 178.

In the vertical structure nonvolatile memory device 1 according to thecurrent embodiment, the gates 150 are configured to have uneven (ornon-planar) structures to increase lengths of the channel layers 140,without increasing transistor size. Thus, reductions in memory cellstring current and threshold voltage, may reduce short channel effectsin the device.

FIGS. 3 through 10 are cross-sectional views for describing a method offabricating the nonvolatile memory device 1 of FIG. 2, according to anexemplary embodiment.

Referring to FIG. 3, a plurality of interlayer insulating layers 110 anda plurality of sacrificial layers 120 are alternately stacked on thesubstrate 100. Each of the sacrificial layers 120 includes a firstsacrificial layer 124 and two second sacrificial layers 122 stackedrespectively on upper and lower surfaces of the first sacrificial layer124. The interlayer insulating layers 110, the first sacrificial layers124 and the second sacrificial layers 122 may be formed of materialshaving different etch selectivity with respect to adjacent sacrificiallayers. The etch selectivity may be quantified as an etch rate of onelayer to another. In the current embodiment, the interlayer insulatinglayers 110 and the second sacrificial layers 122 may be formed ofmaterials having an etch selectivity of about 1:10 to about 1:200 withrespect to the first sacrificial layers 124. The interlayer insulatinglayers 110 may be formed of a material having an etch selectivity ofabout 1:10 to about 1:200 with respect to the second sacrificial layers122. For example, the plurality of interlayer insulating layers 110 maybe formed of a silicon oxide layer. The plurality of first sacrificiallayers 124 may be formed of a silicon nitride layer. The plurality ofsecond sacrificial layers 122 may be formed of a silicon carbide layeror an amorphous carbon layer (ACL).

The number of sacrificial layers 120 may be varied according to thememory device to be fabricated. The larger the number of sacrificiallayers 120, the more the memory cells per unit area. The thicknesses ofthe individual interlayer insulating layers 110 and the individualsacrificial layers 120 may not be completely the same. The uppermostinterlayer insulating layer among the plurality of interlayer insulatinglayers 110 may have a thickness larger than the thicknesses of theunderlying interlayer insulating layers 110.

Referring to FIG. 4, the plurality of interlayer insulating layers 110and the plurality of sacrificial layers 120 may be etched usingphotolithography to form a plurality of channel holes 132 exposing thesubstrate 100. The channel holes 132 may be isolated from each other inthe first and second directions (the x-axis and y-axis directions ofFIG. 2).

Forming the plurality of channel holes 132 may be provided by forming apredetermined mask pattern on the uppermost interlayer insulating layer110 to define the locations of the channel holes 132, andanisotropically etching the stacked structure, including the interlayerinsulating layers 110 and the sacrificial layers 120, by using the maskpattern as an etch mask. Side walls of the plurality of channel holes132 may not be completely perpendicular to the upper surface of thesubstrate 100, since the stacked structure includes at least threedifferent kinds of materials layers. For example, the closer to thesubstrate 100, the smaller the width of the channel holes 132 may be. Ifthe stack structure on the substrate 100 is over-etched during theanisotropic etching process to define the channel holes 132, the uppersurface of the substrate 100 may be recessed to a predetermined depth,as illustrated in FIG. 4.

Referring to FIG. 5, the first sacrificial layers 124 exposed by theplurality of channel holes 132 are partially recessed beyond sidewallsof the channel hole 132. This process may be performed using an etchantthat may selectively etch only the first sacrificial layers 124 withrespect to the interlayer insulating layers 110 and the secondsacrificial layers 122. The dimensions of the protrusions of the channellayers 140 (see FIG. 2) extending in the first direction (the x-axisdirection of FIG. 2) are determined according to the extent to which thefirst sacrificial layers 124 are etched. As a result of the etchingprocess, the channel holes 132 are formed having uneven (non-planar)shapes.

Referring to FIG. 6, a semiconductor material and an insulating materialare sequentially deposited in the channel holes 132, followed by aplanarization process in which the semiconductor material and theinsulating material covering the uppermost interlayer insulating layer110 are removed until the uppermost interlayer insulating layer 110 isexposed to provide channel layers 140 and channel hole insulating layer115. For example, the planarization process may be performed usingchemical mechanical polishing (CMP) or an etch-back process. Forexample, the channel layers 140 may be formed of silicon. The channellayers 140 may be formed as polycrystalline or monocrystalline Siepitaxial layers. The channel hole insulating layers 115 may include anoxide layer such as Undoped Silica Glass (USG), Spin On Glass (SOG) orTonen SilaZene (TOSZ).

A conductive layer may be formed on the uppermost channel layer 140 todefine metal contacts or plugs to be coupled to the bit lines. Forexample, the channel hole insulating layers 115 may be etched from theirtop regions to a predetermined thickness to form trenches, and thetrenches may be filled with conductive layers.

Referring to FIG. 7, the interlayer insulating layers 110 and thesacrificial layers 120 between each two adjacent channel layers 140 areetched to form a plurality of openings 134 exposing the upper surface ofthe substrate 100. Only one of the plurality of openings 134 isillustrated in FIG. 7. The plurality of openings 134 may be formed usingphotolithography.

Referring to FIG. 8, the second sacrificial layers 122 and the firstsacrificial layers 124 exposed by the plurality of openings 134 areremoved.

For example, the second and first sacrificial layers 122 and 124 may beremoved using isotropic etching. An etchant may be permeated between theplurality of interlayer insulating layers 110 through the openings 134.The isotropic etching process may be wet etching or chemical dry etching(CDE). The second sacrificial layers 122 and the first sacrificiallayers 124 may be simultaneously etched using the same kind of etchant.Alternatively, the second sacrificial layers 122 and the firstsacrificial layers 124 may be separately etched one after another usingdifferent etchants.

As a result of removing the plurality of first sacrificial layers 124and the plurality of second sacrificial layers 122 from between theplurality of interlayer insulating layers 110, a plurality of tunnels134T in the openings 134 are formed between the plurality of interlayerinsulating layers 110. The plurality of tunnels 134T expose thesidewalls of the channel layers 140.

Referring to FIG. 9, the gate insulating layer 157 is formed to coverthe surfaces of the plurality of interlayer insulating layers 110 andthe channel layers 140 exposed by the plurality of openings 134. Thegate insulating layer 157 may have a stacked structure in which atunneling insulating layer 152, a charge storage layer 154 and ablocking insulating layer 156 are sequentially stacked on a sidewall ofthe channel layers 140 in the order stated. Then, a conductive materialis deposited into the openings 134 so as to completely fill theplurality of tunnels 134T, which are interconnected with the openings134, on the sidewalls of the channel layers 140, followed by removingthe unnecessary conductive material from the openings 134 until theconductive material remains only within the plurality of tunnels 134T,thus resulting in the gate electrodes 159.

The gate insulating layer 157 and the gate electrodes 159 may be formedusing chemical vapor deposition (CVD) or electroplating. For example,the gate electrodes 159 may be formed of tungsten.

The gates 150 of the plurality of transistors 170 may be respectivelycoupled to the string selection lines SSL, the ground selection linesGSL and the word lines WL0-WLn via contact plugs in the periphery ofcell memory regions. Since the selection transistors 176 and 178includes only one selection transistor, i.e., respectively, a singleground selection transistor GST and a single string selection transistorSST, instead of a pair of transistors, it is sufficient to connect onlyone contact plug to each of the string selection line SSL and the groundselection line GSL. Thus, the overall process may be simplified comparedto when a pair of transistors should be connected to each of theselection lines.

Referring to FIG. 10, the upper surface of the substrate 100 exposed bythe plurality of openings 134 may be doped with impurities to formimpurity regions 105. The impurity regions 105 may be heavily-dopedimpurity regions formed by injecting N⁺-type impurity ions. The processof forming the impurity regions 105 in the upper surface of thesubstrate 100 exposed by the openings 134 may be performed in anypreceding or subsequent processes. The impurity regions 105 may functionas common source regions. The spacers 117 may be formed on the sidewallsof the openings 134 defined in the substrate 100. The spacers 117 may beformed to cover the parts of the gate insulating layers 157 and the gateelectrodes 159 exposed by the openings 134. The spacers 117 may beformed by depositing an insulating layer on the surfaces of the channelhole insulating layers 115 so as to fill the openings 134, and etchingthe insulating layer using, for example, an etch-back process. Theinsulating layer for forming the spacers 117 may include a siliconnitride layer.

Then, a conductive material is deposited between the spacers 117 in theopenings 134 to form conductive lines. The conductive lines mayconstitute the common source lines (CSL) 180 of FIG. 2 connected to theimpurity regions 150, and may be coupled to sources of the groundselection transistors 176. The nonvolatile memory device 1 of FIG. 2 maybe fabricated through the processes described above.

FIGS. 11 and 12 are plan views illustrating the relative positions ofthe channel layers 140 with respect to the bit lines 190, according toexemplary embodiments, in the vertical structure nonvolatile memorydevice.

In some embodiments according to the inventive concept, the channellayers 140 may be in the form of annular pillars filled with the channelhole insulating layers 115, as illustrated in FIG. 11. The bit lines 190may be disposed to completely cover upper ends of the channels layers140, as illustrated in FIG. 1. Alternatively, the bit lines 190 may bedisposed to partially cover the upper ends of the channel layers 140, asillustrated in FIG. 12. Furthermore, as described above with referenceto FIG. 6, the channel layers 140 may be coupled to the bit lines 190via metal contacts or plugs formed from the conductive layers depositedon the channel layers 140.

FIG. 13 is a cross-sectional view of a vertical structure nonvolatilememory device 2 according to another embodiment of the present inventiveconcept.

Referring to FIG. 13, the channel layers 140 have protrusions only inregions adjacent to the gates 150 of the string selection transistor 178and the ground selection transistor 176. This configuration may beimplemented if, for example, in the fabrication processes described withreference to FIGS. 3 to 10, the first sacrificial layer 124 is depositedonly between the uppermost pair and between the lowermost pair of secondsacrificial layers 122 in which the selection transistors 176 and 178are to be defined, during the process described above with reference toFIG. 3. In the nonvolatile memory device 2, the selection transistors176 and 178 have extended channel lengths. Thus, a larger amount ofcurrent may flow in the memory cell strings.

FIGS. 14 through 16 are graphs illustrating the results of simulation ofpotential distribution in the vertical structure nonvolatile memorydevice 2 of FIG. 13.

FIG. 14 illustrates the distributions of potential in the gate of aselection transistor having the uneven structure illustrated in FIG. 13in the first and second directions (x-axis and y-axis directions of FIG.14), as opposed to the distributions of potential in the two gates of apaired-selection transistor structure consisting of a pair oftransistors. The paired-selection transistor structure refers to aselection transistor configuration consisting of a pair of separatetransistors that are serially disposed. FIG. 14 illustrates thedistributions of potential when a voltage of 6V was applied to theselection translator structures whose channel layers include aninsulating layer, a channel layer, and a gate insulating layer, shownfrom left to right in FIG. 14, which are stacked upon one another. Forthe selection transistor having the uneven structure of FIG. 13, ahigher level of potential was distributed in the middle region (B) ofthe uneven structure in the second direction (the y-axis direction ofFIG. 14), compared to the paired-selection transistor structure. Inparticular, in the region of the uneven structure in the coordinates ofabout 0.08 um or more in the first direction (the x-axis direction ofFIG. 14), the potential was maintained as high as 6.0V or greater.

FIG. 15 is a graph illustrating the distributions of potential in anupper region (A) and middle region (B) of each of the selectiontransistor structures in the first direction (the x-axis direction ofFIG. 14). Referring to FIG. 15, in the upper regions (A), there wassubstantially no potential difference between the selection transistorhaving the uneven structure and the paired-selection transistorstructure. However, in the middle region (B) of the selection transistorhaving the uneven structure, the potential level was higher than thepaired-selection transistor structure.

FIG. 16 is a graph illustrating the distributions of potential in theselection transistor structures in the second direction (the y-axisdirection of FIG. 14). Referring to FIG. 16 the selection transistorhaving the uneven structure had a higher potential distribution in themiddle region (B) than the paired-selection transistor structure.Therefore, the vertical structure nonvolatile memory device, accordingto embodiments of the inventive concept, having the uneven structurebetween the gate of the selection transistor and the channel may improvethe control ability of the gate. In addition, the switching performanceof the selection transistor may be improved.

FIG. 17 is a cross-sectional view of a vertical structure nonvolatilememory device 3 according to another embodiment.

Referring to FIG. 17, in the nonvolatile memory device 3, the sides ofthe interlayer insulating layers 110 adjacent to the channel layers 140are recessed in the first direction (an x-axis direction of FIG. 7) withrespect to the gates 150 of the transistors 170 so as to expose surfaceedge portions of the gates 150. The exposed surface edge portions of thegates 150 are covered by the channel layers 140. This configuration maybe implemented if, for example, in the fabrication processes describedwith reference to FIGS. 3 to 10, the first sacrificial layers 124 andthe interlayer insulating layers 110 are formed of the same material ormaterials having substantially the same etch selectivity in an etchantwith respect to the second sacrificial layers 122, and the interlayerinsulating layers 110 are partially removed together with the firstsacrificial layers 124 in the etching process described with referenceto FIG. 5. In the nonvolatile memory device 3 according to the currentembodiment, the transistors 170 may have further extended channellengths.

FIG. 18 is a cross-sectional view of a vertical structure nonvolatilememory device 4 according to another embodiment.

Referring to FIG. 18, in the nonvolatile memory device 4, portions ofthe channel layers 140 associated with the selection transistors 176 and178, have uneven structures in regions adjacent to the gates 150, whichinclude the gate insulating layers 157 and the gate electrodes 159. Eachuneven structure includes two protrusions in upper and lower regions ofthe channel layer 140. This configuration may be implemented if, forexample, in the fabrication processes described with reference to FIGS.3 to 10, the second sacrificial layers 122 on the upper and lowersurfaces of the first sacrificial layers 124 are partially removed,instead of the first sacrificial layers 124, during the processdescribed with reference to FIG. 5. Though only the selectiontransistors 176 and 178 have the uneven structures in FIG. 18, theinventive concept is not limited thereto. For example, the secondtransistors 172 may also have such uneven structures, with multipleprotrusions per gate.

FIG. 19 is a cross-sectional view of a vertical structure nonvolatilememory device 5 according to another embodiment.

Referring to FIG. 19, in the nonvolatile memory device 5, the gates 150of the selection transistors 176 and 178, which include the gateinsulating layers 157 and the gate electrodes 159, have unevenstructures each including a recess in the middle of the gate 150 thatdeepens in the first direction (an x-axis direction of FIG. 9). Spacesbetween the recesses of the gates 150 and the channel layers 140 arefilled with second interlayer insulating layers 112. The secondinterlayer insulating layers 112 may contain a material having adifferent etch selectivity from the first interlayer insulating layers110 disposed between the plurality of first transistors 172 and betweenone of the first transistors 172 and the selection transistors 176 and178. The recesses may be located in the middles of the gates 150 of thetransistors 170 in the second direction (a y-axis direction of FIG. 19,and may also extend in a third direction (a z-axis direction of FIG. 9).The recesses may have a dimension in the first direction (the x-axisdirection of FIG. 9) that is smaller than the dimension of thetransistors 170. Though only the selection transistors 176 and 178 havethe uneven structures in FIG. 19, the inventive concept is not limitedthereto. For example, the second transistors 172 may also have suchuneven structures including insulating layers between the gates 150 andthe channel layers 140.

In the vertical structure nonvolatile memory device 5 according to thecurrent embodiment, each of the selection transistors 176 and 178 isconfigured to include at least two parts interconnected so as to befilled with an electrode material without a void, unlike in a singletransistor without recesses, to form the gate electrode 159 between thefirst interlayer insulating layers 111. In addition, since the gateelectrodes 159 are connected within memory cell strings, wiringprocesses may be simplified, compared to the configuration in which eachselection transistor includes a pair of serially disposed transistors.

FIGS. 20 through 23 are cross-sectional views for describing a method offabricating the vertical structure nonvolatile memory device 5 of FIG.19, according to an exemplary embodiment.

Referring to FIG. 20, the plurality of first and second interlayerinsulating layers 111 and 112, and the plurality of sacrificial layers125 are alternately stacked on the substrate 100 in substantially thesame manner as described above with reference to FIG. 3, except that thesecond interlayer insulating layers 112 are stacked as the second endinsulating layers from the upper and lower surfaces of the stackstructure on the substrate 100, while the first interlayer insulatinglayers 111 constitute the other insulating layers. The first interlayerinsulating layers 111 and the second interlayer insulating layers 112may contain materials having different etch selectivity.

Referring to FIG. 21, the plurality of first interlayer insulatinglayers 111, the plurality of second interlayer insulating layers 112,and the plurality of sacrificial layers 125 are etched in the samemanner as described with reference to FIG. 4, to form the plurality ofchannel holes 132 (see FIG. 4). Then, a semiconductor material and aninsulating material are sequentially deposited in the channel holes 132,followed by chemical mechanical polishing (CMP) or performing anetch-back process to form the channel layers 140 and the channel holeinsulating layers 115 in the channel holes 132. For example, the channellayers 140 may be formed as polycrystalline or monocrystalline Siepitaxial layers.

Referring to FIG. 22, the plurality of first interlayer insulatinglayers 111, the plurality of second interlayer insulating layers 112 andthe plurality of sacrificial layers 125 between each two adjacentchannel layers 140 are etched to form a plurality of openings 134exposing the upper surface of the substrate 100. Then, the plurality ofsacrificial layers 125 exposed by the plurality of openings 134 areremoved, and the second interlayer insulating layers 112 are partiallyremoved. The sacrificial layers 125 and the second interlayer insulatinglayers 112 may be simultaneously etched using the same kind of etchant.Alternatively, the sacrificial layers 125 and the second interlayerinsulating layers 112 may be separately etched one after another usingdifferent kinds of etchants.

As a result, a plurality of tunnels 134T interconnected with theopenings 134 are formed between adjacent first interlayer insulatinglayers 111. Sidewalls of the channel layers 140 are exposed by thetunnels 134T. The second interlayer insulating layers 112 may bepartially etched to have dimensions in the first direction (the x-axisdirection of FIG. 19) that are smaller than the dimensions of the firstinterlayer insulating layers 111.

Referring to FIG. 23, after the processes described above with referenceto FIG. 9 are performed, the upper surface of the substrate 100 exposedby the openings 134 is doped with impurities in a similar manner asdescribed above with reference to FIG. 10, to form impurity regions 105.Then, an insulating layer is deposited to form spacers 117 on thesidewalls of the openings 134 defined in the substrate 100. Theinsulating layer for forming the spacers 117 may include a siliconnitride layer.

Then, a conductive material is deposited between the spacers 117 in theopenings 134 to form conductive lines 180 (see FIG. 19). The conductivelines 180 may constitute the common source lines (CSL) 180 of FIG. 19,and may be coupled to sources of the ground selection transistors 172.The nonvolatile memory device 5 of FIG. 19 may be fabricated through theprocesses described above.

In the nonvolatile memory device according to embodiments of the presentinventive concept, channel layers may have a macaroni-like cylindricalstructure surrounding an insulating pillar. However, the inventiveconcept is not limited to the structure of the channel layers. Forexample, channel layers may be in the form of lines. For example, linearchannel layers may be formed on the sidewalls of insulating pillars.

FIG. 24 is a block diagram illustrating a nonvolatile memory device 700according to an exemplary embodiment.

Referring to FIG. 24, in the nonvolatile memory device 700, a NAND cellarray 750 may be coupled to a core circuit unit 770. For example, theNAND cell array 750 may include at least one of the nonvolatile memorydevices 1-5 respectively described above with reference to FIGS. 2, 13,17, 18 and 19. The core circuit unit 770 may include a control logic771, a row decoder 772, a column decoder 773, a sense amplifier 774, anda page buffer 775.

The control logic 771 may communicate with the row decoder 772, thecolumn decoder 773, and the page buffer 775. The row decoder 772 maycommunicate with the NAND cell array 750 via a plurality of stringselection lines SSL, a plurality of word lines WL, and a plurality ofground selection lines GSL. The column decoder 773 may communicate withthe NAND cell array 750 via a plurality of bit lines BL. The senseamplifier 774 may be connected to the column decoder 733 to receive anoutput from the column decoder 773 when a signal is output from the NANDcell array 750.

For example, the control logic 771 may transmit a row address signal tothe row decoder 772, and the row decoder 772 may decode the row addresssignal and transmit the same to the NAND cell array 750 via the stringselection lines SSL, the word lines WL, and the ground selection linesGSL. The control logic 771 may transmit a column address signal to thecolumn decoder 773 or the page buffer 775, and the column decoder 773may decode the column address signal and transmit the same to the NANDcell array 750 via the bit lines BL. Signals from the NAND cell array750 may be transmitted to the sense amplifier 773 via the column decoder774, and be amplified in the sense amplifier 773 and transmitted throughthe page buffer 775 to the control logic 771.

FIG. 25 is a schematic view illustrating a memory card 800 according toan exemplary embodiment.

Referring to FIG. 25, the memory card 800 may include a controller 810and a memory unit 820, which are installed in a housing 830. Thecontroller 810 and the memory unit 820 may exchange electrical signals.For example, the memory unit 820 and the controller 810 may exchangedata according to a command from the controller 810. The memory card 800may store data in the memory unit 820 or may externally output data fromthe memory unit 820.

For example, the memory unit 820 may include at least one of thenonvolatile memory devices 1-5 respectively described above withreference to FIGS. 2, 13, 17, 18 and 19. The memory card 800 may be usedas a data storage medium of various types of portable appliances. Forexample, the memory card 800 may include a multimedia card (MMC) or asecure digital (SD) card.

FIG. 26 is a block diagram illustrating an electronic system 900according to an exemplary embodiment.

Referring to FIG. 26, the electronic system 900 may include a processor910, an input/output unit 930, and a memory unit 920. Data communicationbetween the processor 910, the input/output unit 930 and the memory unit920 may be conducted via a bus 940. The processor 910 may executeprograms and control the electronic system 900. The input/output unit930 may be used to input data to or output data from the electronicsystem 900. The electronic system 900 may be connected to an externaldevice, for example, a personal computer or a network, via theinput/output unit 930 to exchange data with the external device. Thememory unit 920 may store codes and data for operating the processor910. For example, the memory unit 920 may include at least one of thenonvolatile memory devices 1-5 respectively described above withreference to FIGS. 2, 13, 17, 18 and 19.

The electronic system 900 may constitute various types of electroniccontrollers including the memory unit 920. For example, the electronicsystem 900 may be used in a mobile phone, an MP3 player, a navigationdevice, a solid state disk (SSD), or other household appliances.

While the inventive concept has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the following claims.

What is claimed is:
 1. A vertical structure nonvolatile memory devicecomprising: a channel layer extending in a vertical direction on asubstrate; and a memory cell string comprising a plurality oftransistors disposed on the substrate in the vertical direction along avertical sidewall of the channel layer, wherein at least one of theplurality of transistors includes at least one recess in a gate of thetransistor into which at least one protrusion, comprising the channellayer, extends.
 2. The vertical structure nonvolatile memory device ofclaim 1, wherein the plurality of transistors of the memory cell stringcomprise a plurality of memory cell transistors, and at least oneselection transistor disposed at one end or at both ends of the memorycell string.
 3. The vertical structure nonvolatile memory device ofclaim 2, wherein the at least one recess and at least one protrusion areincluded in the at least one selection transistor.
 4. The verticalstructure nonvolatile memory device of claim 1, wherein an entire widthof the channel layer protrudes into the recess and is conformally on asurface of the recess.
 5. The vertical structure nonvolatile memorydevice of claim 1, wherein the at least one protrusion only protrudesinto a middle region of the gate between uppermost and lowermostsurfaces of the gate adjacent to respective interlayer insulatinglayers.
 6. The vertical structure nonvolatile memory device of claim 5,wherein the recess has a vertical dimension that is greater than all ofa remaining vertical dimension of the gate outside the recess.
 7. Thevertical structure nonvolatile memory device of claim 5, wherein the atleast one recess and the at least one protrusion comprises first andsecond recesses and first and second protrusions disposed in first andsecond regions of the gate.
 8. The vertical structure nonvolatile memorydevice of claim 1, the structure further comprising: a first interlayerinsulating layer between immediately adjacent gates; and a secondinterlayer insulating layer in the recess between a gate electrode ofthe gate and layer.
 9. The vertical structure nonvolatile memory deviceof claim 8, wherein the second interlayer insulating layer between thechannel layer and the gate electrode has an etch selectivity differentfrom that of the first interlayer insulating layer.
 10. The verticalstructure nonvolatile memory device of claim 8, wherein the firstinterlayer insulating layeris recessed from sides of the gates adjacentto the channel layer, in the same direction as the direction in whichthe at least one protrusion extends into the recess.
 11. The verticalstructure nonvolatile memory device of claim 1, wherein the gatecomprises: a tunneling insulating layer, a charge storage layer and ablocking insulating layer that are sequentially stacked on the channellayer; and a gate electrode.
 12. The vertical structure nonvolatilememory device of claim 11, wherein the charge storage layer comprises atleast one selected from the group consisting of silicon nitride,polysilicon and fine particles of a conductor in insulator.
 13. Thevertical structure nonvolatile memory device of claim 11, wherein thetunneling insulating layer and the blocking insulating layer comprisematerials having a larger bandgap than a material of the charge storagelayer, and the blocking insulating layer has a dielectric constanthigher than that of the tunneling insulating layer.
 14. The verticalstructure nonvolatile memory device of claim 1, wherein the channellayer comprises an annular pillar region, and the annular pillar regionof the channel layer is filled with an insulating pillar.
 15. Thevertical structure nonvolatile memory device of claim 1, furthercomprising: a bit line coupled to one terminal of the memory cellstring; and a common source line coupled to a terminal of the memorycell string opposite to the terminal coupled to the bit line.
 16. Thevertical structure nonvolatile memory device of claim 1, furthercomprising: a plurality of conductive lines disposed between adjacentmemory cell strings; and spacers disposed on sidewalls of the memorycell strings to insulate the conductive lines from the memory cellstrings.
 17. A vertical structure nonvolatile memory device comprising:a plurality of transistors in a memory cell string, each including arespective gate electrode; a recess in at least one of the gateelectrodes defining a portion of a non-planar surface of the at leastone gate electrode; and a channel layer protruding into the recess andconformally on the portion of the non-planar surface.
 18. The verticalstructure nonvolatile memory device according to claim 17 wherein the atleast one of the gate electrodes comprises only first and secondselection transistors at both ends of the memory cell string.
 19. Thevertical structure nonvolatile memory device according to claim 17,wherein the recess comprises a first recess and the portion comprises afirst portion, the device further comprising: a second recess in theleast one of the gate electrodes including the at least one recessdefining a second portion of the non-planar surface therein, wherein thechannel layer protrudes into the second recess and is conformally on thesecond portion of the non-planar surface.
 20. A system comprising: amemory including a vertical structure nonvolatile memory devicecomprising: a plurality of transistors in a memory cell string, eachincluding a respective gate electrode; a recess in at least one of thegate electrodes defining a portion of a non-planar surface of the atleast one gate electrode; and a channel layer protruding into the recessand conformally on the portion of the non-planar surface, the systemfurther comprising: a processor configured to communicate with thememory via a bus; and an input/output unit configured to communicatewith the bus.